Strand tension control

ABSTRACT

The tension in advancing strand materials is controlled by an apparatus in which the restraint imposed upon a strand engaging a pulley or cylinder is controllably varied by changes in the flux density of an electromagnetic field. Cooperating poles which direct the flux of the field are movable into and out of axial alignment and movable toward one another and apart, to facilitate accurate control over the flux density. The tension control apparatus is particularly applicable to textile yarn processing apparatus such as false twist texturing apparatus and to winding apparatus in which strand material is supplied from a creel.

[ Mar. 19, 1974 TOiiEidN PATENTS OR APPLICATIONS 189,905 12/1922 Great Britain........................ 242/45 15 71" S/1943"" Swit'irland Primary Examiner-Stanley N. Gilreath Attorney, Agent, or Firm-Parrott, Bell, Seltzer, Park & Gibson ABSTRACT The tension in advancing strand materials is controlled by an apparatus in which the restraint imposed upon a strand engaging a pulley or cylinder is controllably varied by changes in the flux density of an electromagnetic field. Cooperating poles which direct the flux of 19 Claims, 5 Drawing Figures the field are movable into and out of axial alignment and movable toward one another and apart, to facilitate accurate control over the flux density. The tension control apparatus is particularly applicable to textile yarn processing apparatus such as false twist texturing apparatus and to winding apparatus in which strand material is supplied from a creel.

57/34 HS; 310/93, DlG. 2

'IIIIIIIIIIIIJ 242/155 M UX 242/155 M X l-leffelfinger Parker............. Roughsedge Pierce et a1...... Bancroft..........

United States Patent White STRAND TENSION CONTROL [76] Inventor: Eugene F White, 660-South Church Streets, Monroe, NC. 28110 [22] Filed:

Feb. 1, 1973 21 Appl. No.: 328,502

[52] U.S. Cl........ 242/155 M, 57/34 HS, 242/131.1,

[58] Field of Search.......

[5 6] References Cited UNITED STATES PATENTS STRAND TENSION CONTROL Apparatus and processes which involve the handling of strand materials such as textile yarn have long required controlled tension conditions in the strand materials in order to achieve the highest quality result. Heretofore, the commercially practicable solutions to tension control have conventionally relied upon the imposition of frictional drags on an advancing strand. By way of example, two types of tension control heretofore employed have been opposed pairs of discs, biased one toward the other and with the yarn passing therebetween, and interdigitating fingers which cause an advancing strand to follow a sinuous path.

The difficulties and deficiencies arising from such frictional drag tension controls have long been recognized. In certain apparatus and operations, the desired high quality is sufficiently impaired by such frictional drag tension control as to require the adoption of other approaches. Particularly in false twist texturing machines, tension control has been accomplished by the use of positive yarn feed arrangement such as Casablanca rolls driven to overfeed the strand material. Such positive feeding arrangements have been more satisfactory than frictional drag tension controls but do not accommodate fluctuations in tension conditions such as conventionally occur due to fluctuation in the characteristics of the strand material being handled and in the operating condition of the apparatus.

With the above problems in mind, it is an object of this invention to accomplish control over the tension in an advancing strand of material while accommodating extremely accurate adjustment of the controlled tension. In realizing this object of this invention, the advancing strand material to be subjected to tension control is passed in engagement with a rotor and the rotor is restrained against being rotatably driven by advancement of the strand. The restraint imposed on the rotor is established by the adjustment of three distinct variables, namely the characteristics of an electrical current flowing through a coil, the alignment of poles directing the flux of the resulting electromagnetic field, and the spacing of those poles.

Yet a further object of this invention is to improve the processing of strand materials such as textile yarns by facilitating more uniform imposition of tension controls in processing apparatus such as false twist texturing machines and beamers. In realizing this object of the present invention, a choice is made available between open and closed loop control systems which may operate on individual thread lines or on multiple parallel thread lines to provide individual or grouped control over the tension in advancing strand materials.

Some of the objects of the invention having been stated, other objects will appear as the description proceeds, when taken in connection with the accompanying drawings, in which FIG. 1 is an elevation view, in section, through a tension control apparatus in accordance with this invention;

FIG. 2 is a schematic perspective view illustrating the use of tension control apparatus of FIG. 1 in a closed loop tension control system;

FIG. 3 is an exploded perspective view of the apparatus of FIG. 1;

FIG. 4 is a schematic elevation view of a textile yarn processing apparatus incorporating the tension control of FIGS. 1 3; and

FIG. 5 is a schematic elevation view of a textile yarn beamer incorporating the tension control apparatus of FIGS. 1 3.

The apparatus of this invention will be described hereinafter with particular reference to the accompanying drawings. While the description and the drawings set forth the best mode presently contemplated for this invention, it is to be understood that this invention is viewed as having a broad utility and is not restricted to the specific construction and uses herein described and illustrated. Accordingly, the description and illustrations are to be taken as a broad teaching of this invention rather than a restrictive teaching.

In accordance with this invention, the apparatus for controlling the tension of advancing strand materials comprises coil means generally indicated at 10 mounted within the two halves l 1, 12 of a housing. The coil means 10 is formed by winding suitable electrical conductors 14 on a spool or coil form 15 which is then secured to one housing portion 1 1. Two conductors 16, 18 pass from the coil 10 through the housing 11, 12 for connection with an appropriate source of electricity as will be described more fully hereinafter. As will be understood, an electromagnetic field is generated upon energization of the coil means 10. The flux density of the electromagnetic field may be varied by varying the characteristics of the electrical current flowing through the coil 10.

Mounted within the generally annular coil 10 are a pair of pole means 19, 21 for directing the flux of the electromagnetic field generated by the coil 10. One of the poles 19 is mounted from the one housing portion 11 which supports the spools 15 of the coil 10, while the other pole 21 is mounted from the other housing portion 12. In each instance, the poles 19, 21 are constructed to have generally circular configurations about a central axis and to define a plurality of spaced apart parallel segments 20, 22. In the form illustrated, each of the segments 20, 22 has a three dimensional configuration and extends radially of the respective pole, axially of the respective pole and circumferentially of the respective pole (see FIG. 3). In the sense herein used, the reference to the segments 20, 22 being parallel is to the axial protrusion of the segments in the direction of the central axis of the generally circular poles 19, 21. As will be understood, the segments 20, 22 also are uniformly spaced apart about the circumferences of the poles 19, 21.

In accordance with this invention, the poles 19, 21 are mounted in predetermined relation of one to another with the segments 20, 22 in opposition (FIGS. 1 and 3). In order to provide for certain of the adjustment features of this invention, at least one of the poles is mounted for movement relative to the other thereof. Such adjusting movement in accordance with this invention includes movement of segments 20, 22 into and out of axial alignment and movement thereof toward one another and apart. Thus two spacing characteris tics are controlled in order to determine the directing of the flux of the electromagnetic field.

In particular, one pole 19 is fixedly supported from the one housing portion 11. The other pole 21 is mounted from the other housing portion 12 for rotation relative thereto. The circular pole 21 has a central plug 24 mounted therewithin which penetrates through the other housing portion 12 and has a flattened stub end which may be gripped by a wrench or other appropriate tool. By rotation of the central plug 24, the rotary position of the second pole 21 may be changed so as to move the segments 22 into and out of axial alignment with the segments of the first pole 19. Additionally, the position of the other housing portion 12 relative to the one housing portion 11 is determined in part by three mounting screws 25 which penetrate the housing portion 12 and engage a bearing mounting member 26 to which the one housing portion 11 is secured by a corresponding number of screws 28. By tightening the screws 25, advantage may be taken over the flexibility of the sheet material which forms the other housing portion 12, flexing the housing and moving the segments 22 toward or away from the segment 20 of the first pole 19.

The apparatus in accordance with this invention includes rotor means for engaging a strand to be controlled and for imposing thereon a restraint determined by the flux density of the electromagnetic field between the poles 19, 21. The rotor means includes a rotatably supported strand engaging pulley 29 secured to a mounting shaft 30. The mounting shaft 30 is supported to lie along the common axis of the poles 19, 21, by means of spaced anti-friction bearings generally indicated at 31 and 32. The outer races of the anti-friction bearings 31, 32 are received and supported by the bearing support block 26 to which the first pole 19 is secured.

in order to impose a restraint on the pulley 29 and an advancing strand driving the pulley in rotation, the rotor means includes a flux cutting disc 34 secured to the terminal end of the shaft 30 which lies within the housing portions 11, 12. The flux cutting disc 34 is disposed between the poles 19, 21 and on rotation, passes through the electromagnetic field which has been directed to extend between the segments 20, 22 of the poles 19, 21. The flux cutting disc 34 is formed of an electrically conductive material and preferably of a ferrous material. By proper selection of the hysteresis properties of the disc material, tension may be maintained constant through a range of rotational speeds of the shaft 30.

As will be understood, the restraint imposed on the pulley 29 and an advancing strand otherwise driving the pulley in free rotation is determined by the characteristics of the electrical current flowing through the windings 14, by the relative axial alignment of the segments 20, 22 of the poles 19, 21 and by the relative axial distances between the poles 19, 21 and the flux cutting disc 34. Thus, an installation employing the tension control apparatus of this invention has available three separate variables by which to control the tension in the strand material. Coordinated use of the three variables can assure that accurate control is achieved and maintained either for an individual advancing strand or for a group of advancing strands.

In particular, it is known that the restraint imposed on a rotor such as that of the apparatus of this invention as the result of cutting of the flux of an electromagnetic field may be graphically represented as a curve plotting restraint against a characteristic of the applied electrical current. By varying the axial alignment of the segments 20, 22 and the spacing therebetween, the slope of that curve may be redefined. Thus, a plurality of tension controls as illustrated in FIGS. 1 and 3 may be brought to a uniform and closely matched response. This important feature of this invention accommodates either open loop or closed loop control of varying numbers of apparatus.

A closed loop control arrangement is illustrated in FIG. 2. As there shown, the conductors 16, 18 through which electrical current is supplied to the coil of an apparatus in accordance with this invention are connected with a current controller 35 which may be a known type of device. Sensor means 36 are provided for engaging an advanding strand S and for responding to fluctuations in the tension conditions of the strand S by providing an electrical output which is delivered to the controller 35. Details of the electronic circuitry and structure of the controller 35 and the sensor 36 are not disclosed herein, as is anticipated that such structures may be selected from among known devices. In the closed loop control system, electrical current such as line voltage delivered to the controller 35 from an appropriate source is modified as function of conditions detected by the sensor 36 and is applied to the coil 10 of an associated apparatus to increase or decrease the restraint imposed as may be required for establishing a desired tension condition. It is contemplated that a plurality of strands may be sensed and an average signal derived for controlling as many as several hundred strands. Such an averaging system reduces costs where the strand to strand variation which results is acceptable.

An open loop control system would be somewhat similar to the closed loop control system described hereinabove, but would replace the sensor 36 with a set point means such as a potentiometer 38. By means of the potentiometer 38, the characteristics of the electrical current delivered through the controller 35 could be established and maintained at a desired setting. As will be understood, such an open loop control may readily be applied to a plurality of strands delivered in parallel, by connecting the conductor 16, 18 of a plurality of coils 10 to a common controller 35. While a similar multiple connection may be employed for an open loop control system as described hereinabove, it is often preferable to provide an individual sensor 36 for each strand S where closed loop control is desired.

The apparatus of this invention as described to this point is applicable with particular benefit to two types of textile machinery, namely thermoplastic yarn texturing machines of the false twist type and beaming apparatus in which a plurality of yarns are wound onto a common package. A false twist texturing machine of generally known type is illustrated schematically in FIG. 4, where yarn Y is delivered from a supply package 39 and is directed along a predetermined path of travel which extends adjacent a heater 40. The yarn Y passes through a false twist spindle 41 and is wound into a take-up package 42. The construction and operation of such a false twist texturing machine is generally well known and will not be described in detail herein.

In order to facilitate achievement of the desired textured effect for the yarn Y, this invention is applied by mounting an apparatus as described hereinabove as a guide pulley 29 intermediate the supply package 39 and the heater 40. Thus, controlled restraint may be applied to the yarn Y as the same is drawn along the predetermined path of travel. Particularly where a closed loop control system is employed as described hereinabove, desired tension conditions within the zone adjacent the heater 40 are readily achieved and maintained. Thus, desired characteristics are more reliably imparted to the yarn being textured. By deliberately programming a controller to accomplish variation in signals to the tension control apparatus, production of a novelty effect occurs.

A beamer for textile yarn (as illustrated schematically in FIG. 5) conventionally employs a creel 44 in which a pluralityof packages of strand material are mounted. A plurality of strands are delivered from the creel toward a beam 45, which is rotated to draw the strands from the creel and wind them about the beam 45 into a package. This invention is applied to a beamer by locating the strand engaging pulleys 29 immediately adjacent the creel so as to impose a controlled restraint on the strands as the same advance from the creel toward the beam 45. Where a closed loop control is employed, the sensor 36 preferably is mounted closely adjacent the beam 45, to sense the tension condition in the strands immediately before formation thereof into a package.

In the drawings and specification, there has been set forth a preferred embodiment of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

That which is claimed is: 1. Apparatus for controlling the tension in advancing strand material comprising:

coil means for generating an electromagnetic field of controllably variable flux density and having a first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to a common axis,

mounting means for mounting said pole means in predetermined relation one to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart, and

rotor means for engaging a strand to be controlled and for imposing thereon a restraint determined by the flux density of the electro-magnetic field between said pole means, said rotor means having a strand engaging pulley means for engaging an advancing strand to be controlled and supported for rotation about said common axis and flux cutting means secured to said pulley means for rotation therewith and positioned for rotation between said pole means, said rotor means being restrained against being rotatably driven by advancement of the strand engaging said pulley means due to rotation of said flux cutting means through the electromagnetic field.

2. Apparatus according to claim 1 wherein each of said pole means is of generally circular configuration about a central axis and said pole means are mounted with said central axes aligned on a common axis, and further comprising bearing means for supporting said rotor means for rotation about said axis.

3. Apparatus according to claim 2 wherein said pulley means and said flux cutting means are spaced axially along said common axis one from the other and wherein said rotor means further has a shaft extending along said common axis and operatively connecting said pulley means and said flux cutting means.

4. Apparatus according to claim 2 wherein one of said pole means is fixedly disposed along said common axis between said pulley means and said flux cutting means and said mounting means supports the other of said pole means for said axial alignment movement and said movement of said segments toward one another and apart.

5. Apparatus according to claim 1 wherein each of said pole means is of generally circular configuration about a central axis, said pole means are mounted with said central axes aligned on a common axis, and said segments of said pole means extend parallel one to another and to said common axis.

6. Apparatus according to claim 5 wherein said segments of said pole means are uniformly spaced about the circumferences of said pole means and further wherein said mounting means supports one of said pole means for rotation about said central axis thereof and thereby for said axial alignment movement of said segments.

7. Apparatus according to claim 6 wherein said mounting means fixedly supports the other of said pole means and supports said one pole means for movement along said common axis and thereby for said movement of said segments toward one another and apart.

8. Apparatus according to claim 1 further comprising electrical control means electrically connected with said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetic field having a flux density dependent in part upon the electrical energization of said coil means by said control means.

9. Apparatus according to claim 8 wherein said control means comprises set point means for establishing a predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on an engaged advancing strand.

10. Apparatus according to claim 8 wherein said control means comprises sensor means for detecting the tension level of the strand engaging said pulley means and further wherein said control means responds to sensed variations in tension level by varying the level of electrical energization as a closed loop control over the restraint imposed on an engaged advancing strand.

11. In a textile yarn processing apparatus having means for advancing thermoplastic strand materials along a predetermined path of travel, heater means disposed at a predetermined location along the path oftravel for heating an advancing strand and thereby for setting the strand in a desired condition, and twisting means disposed adjacent the heater means for inserting twist into the heated strand, the improvement therewith of means for protecting against undesirable excessive variation in the desired condition of the strand and comprising:

rotor means having pulley means supported adjacent the heater means for engaging the strand in advance of the heater means and the twisting means and for rotation about a common axis in response to advancement of the engaged strand and having flux cutting means secured to said pulley means for rotation therewith about said axis,

coil means for generating an electromagnetic field of controllably variable flux density and having first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to said axis, and

mounting means for mounting said pole means on opposite sides of said flux cutting means and in predetermined relation on to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart,

the controlled flux density of the electromagnetic field imposing a controlled restraint on rotation of the rotor means and thereby maintaining tension conditions in the strand more uniform during twisting and heating of the strand so as to facilitate consistent attainment of the desired condition.

12. Apparatus according to claim 11 further comprising electrical control means electrically connected with said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetic field having a flux density dependent in part upon the electrical energization of said coil means by said control means.

13. Apparatus according to claim 12 wherein said control means comprises set point means for establishing a predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on an engaged advancing strand.

14. Apparatus according to claim 12 wherein said control means comprises sensor means for detecting the tension level of the strand engaging said pulley means and further wherein said control means responds to sensed variations in tension level by varying the level of electrical energization as a closed loop control over the restraint imposed on an engaged advancing strand.

15. In an apparatus having creel means for receiving and supporting a plurality of packages of strand material and for delivering a plurality of strands along predetermined paths of travel, and winding means disposed at a predetermined location along the paths of travel for drawing strands from the creel means and for winding the strands about a beam, the improvement therewith of means for protecting against undesirable excessive variation in the tension desired condition of the strands and including a number of tension control apparatus corresponding to the number of the strands, each tension control apparatus comprising:

rotor means having pulley means supported adjacent the creel means for engaging a corresponding one strand as the strand is drawn from the creel means and for rotation about a common axis in response to advancement of the engaged strand and having flux cutting means secured to said pulley means for rotation therewith about said axis, coil means for generating an electromagnetic field of controllably variable flux density and having first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to said axis, and

mounting means for mounting said pole means on opposite sides of said flux cutting means and in predetermined relation one to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart,

the controlled flux density of the electromagnetic field imposing a controlled restraint on rotation of the rotor means and thereby maintaining tension conditions in the strand more uniform during winding of the strand.

16. Apparatus according to claim 15 further comprising electrical control means electrically connected with each of said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetic field having a flux density dependent in part upon the electrical energization of said coil means by said control means.

17. Apparatus according to claim 16 wherein said control means comprises set point means electrically connected with a plurality of said coil means for establishing a common predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on the corresponding engaged advancing strands.

18. Apparatus according to claim 16 wherein said control means comprises sensor means for detecting the tension in a plurality of strands and further wherein said control means responds to sensed variations in average tension level in the plurality of strands by varying the level of electrical energization of a group of said coil means as an averaging control over the restraint imposed on the advancing strands.

19. Apparatus according to claim 16 wherein said control means comprises a number of sensor means corresponding to the number of strands, each sensor means detecting the tension level of the corresponding one strand engaging the corresponding one pulley means and further wherein said control means responds to sensed variations in tension level in individual strands by varying the level of electrical energization of the corresponding one coil means as a closed loop control over the restraint imposed on the corresponding engaged advancing strand. 

1. Apparatus for controlling the tension in advancing strand material comprising: coil means for generating an electromagnetic field of controllably variable flux density and having a first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to a common axis, mounting means for mounting said pole means in predetermined relation one to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart, and rotor means for engaging a strand to be controlled and for imposing thereon a restraint determined by the flux density of the electro-magnetic field between said pole means, said rotor means having a strand engaging pulley means for engaging an advancing strand to be controlled and supported for rotation about said common axis and flux cutting means secured to said pulley means for rotation therewith and positioned for rotation between said pole means, said rotor means being restrained against being rotatably driven by advancement of the strand engaging said pulley means due to rotation of said flux cutting means through the electromagnetic field.
 2. Apparatus according to claim 1 wherein each of said pole means is of generally circular configuration about a central axis and said pole means are mounted with said central axes aligned on a common axis, and further comprising bearing means for supporting said rotor means for rotation about said axis.
 3. Apparatus according to claim 2 wherein said pulley means and said flux cutting means are spaced axially along said common axis one from the other and wherein said rotor means further has a shaft extending along said common axis and operatively connecting said pulley means and said flux cutting means.
 4. Apparatus according to claim 2 wherein one of said pole means is fixedly disposed along said common axis between said pulley means and said flux cutting means and said mounting means supports the other of said pole means for said axial alignment movement and said movement of said segments toward one another and apart.
 5. Apparatus according to claim 1 wherein each of said pole means is of generally circular configuration about a central axis, said pole means are mounted with said central axes aligned on a common axis, and said segments of said pole means extend parallel one to another and to said common axis.
 6. Apparatus according to claim 5 wherein said segments of said pole means are uniformly spaced about the circumferences of said pole means and further wherein said mounting means supports one of said pole means for rotation about said central axis thereof and thereby for said axial alignment movement of said segments.
 7. Apparatus according to claim 6 wherein said mounting means fixedly supports the other of said pole means and supports said one pole means for movement along said common axis and thereby for said movement of said segments toward one another and apart.
 8. Apparatus according to claim 1 further comprising electrical control means electrically connected with said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetIc field having a flux density dependent in part upon the electrical energization of said coil means by said control means.
 9. Apparatus according to claim 8 wherein said control means comprises set point means for establishing a predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on an engaged advancing strand.
 10. Apparatus according to claim 8 wherein said control means comprises sensor means for detecting the tension level of the strand engaging said pulley means and further wherein said control means responds to sensed variations in tension level by varying the level of electrical energization as a closed loop control over the restraint imposed on an engaged advancing strand.
 11. In a textile yarn processing apparatus having means for advancing thermoplastic strand materials along a predetermined path of travel, heater means disposed at a predetermined location along the path of travel for heating an advancing strand and thereby for setting the strand in a desired condition, and twisting means disposed adjacent the heater means for inserting twist into the heated strand, the improvement therewith of means for protecting against undesirable excessive variation in the desired condition of the strand and comprising: rotor means having pulley means supported adjacent the heater means for engaging the strand in advance of the heater means and the twisting means and for rotation about a common axis in response to advancement of the engaged strand and having flux cutting means secured to said pulley means for rotation therewith about said axis, coil means for generating an electromagnetic field of controllably variable flux density and having first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to said axis, and mounting means for mounting said pole means on opposite sides of said flux cutting means and in predetermined relation on to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart, the controlled flux density of the electromagnetic field imposing a controlled restraint on rotation of the rotor means and thereby maintaining tension conditions in the strand more uniform during twisting and heating of the strand so as to facilitate consistent attainment of the desired condition.
 12. Apparatus according to claim 11 further comprising electrical control means electrically connected with said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetic field having a flux density dependent in part upon the electrical energization of said coil means by said control means.
 13. Apparatus according to claim 12 wherein said control means comprises set point means for establishing a predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on an engaged advancing strand.
 14. Apparatus according to claim 12 wherein said control means comprises sensor means for detecting the tension level of the strand engaging said pulley means and further wherein said control means responds to sensed variations in tension level by varying the level of electrical energization as a closed loop control over the restraint imposed on an engaged advancing strand.
 15. In an apparatus having creel means for receiving and supporting a plurality of packages of strand material and for delivering a plurality of strands along predetermined paths of travel, and winding means disposed at a predetermined location along the paths of travel for drawing strands from the creel means and for winding the strands about a beam, the improvement therewith of means for protecting against undesirable excessive variation in the tension desired condition of the strands and including a number of tension control apparatus corresponding to the number of the strands, each tension control apparatus comprising: rotor means having pulley means supported adjacent the creel means for engaging a corresponding one strand as the strand is drawn from the creel means and for rotation about a common axis in response to advancement of the engaged strand and having flux cutting means secured to said pulley means for rotation therewith about said axis, coil means for generating an electromagnetic field of controllably variable flux density and having first and second pole means for directing the flux of the field, each of said pole means having a plurality of spaced apart segments and the segments being parallel one to another and to said axis, and mounting means for mounting said pole means on opposite sides of said flux cutting means and in predetermined relation one to the other with said segments in opposition and for mounting at least one of said pole means for flux density adjusting movement relative to the other thereof, said mounting means supporting said pole means for movement of said segments into and out of axial alignment and for movement thereof toward one another and apart, the controlled flux density of the electromagnetic field imposing a controlled restraint on rotation of the rotor means and thereby maintaining tension conditions in the strand more uniform during winding of the strand.
 16. Apparatus according to claim 15 further comprising electrical control means electrically connected with each of said coil means for controllably electrically energizing said coil means and thereby for generating an electromagnetic field having a flux density dependent in part upon the electrical energization of said coil means by said control means.
 17. Apparatus according to claim 16 wherein said control means comprises set point means electrically connected with a plurality of said coil means for establishing a common predetermined desired level of electrical energization and for maintaining such level as an open loop control over the restraint imposed on the corresponding engaged advancing strands.
 18. Apparatus according to claim 16 wherein said control means comprises sensor means for detecting the tension in a plurality of strands and further wherein said control means responds to sensed variations in average tension level in the plurality of strands by varying the level of electrical energization of a group of said coil means as an averaging control over the restraint imposed on the advancing strands.
 19. Apparatus according to claim 16 wherein said control means comprises a number of sensor means corresponding to the number of strands, each sensor means detecting the tension level of the corresponding one strand engaging the corresponding one pulley means and further wherein said control means responds to sensed variations in tension level in individual strands by varying the level of electrical energization of the corresponding one coil means as a closed loop control over the restraint imposed on the corresponding engaged advancing strand. 